The flutter of a thin flat-delta wing at transonic speed was investigated by fluid-structure interaction (FSI) analysis, which is based on the open-source software. The analysis model was composed of fluid solver SU2, structure solver CalculiX, and coupler preCICE library. The FSI coupling of both solvers was performed in a partitioned approach. The software and libraries were built on a cloud computing system in Hokkaido University. It was found that self-induced oscillation of the delta wing is induced by the shock wave and elastic deformation in the transonic regime.The primary frequency of the oscillation was approximately 20 Hz for all speeds considered herein. However, the eigenfrequencies of the present condition of the delta wing, which are 9.62, 36.69, 51.22, 88.94, etc., did not correspond to the oscillation frequency. The phase delay of aerodynamic force for the deformation of the delta wing appeared in the oscillation. It was indicated that the oscillation is amplified by the aerodynamic force at the low deformation phase, and that is attenuated at a high deformation phase. In other words, in one cycle, the wing is in an unstable state by receiving the energy from fluid flow at the low deformation and is in a stable state by passing the energy to fluid flow at high deformation. When this energy transfer is equilibrated, the oscillation reaches the limit cycle. It was found that this behavior of the delta wing at the transonic speed is attributed to the shock wave and elastic deformation, i.e., coupling between flow and structure.
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